One known example of a structure of fixedly fastening two members for transmitting torque is a structure in which a friction plate is wedged between the fastened surfaces of the two members being fastened, and the two members are fixed in a fastened manner by a bolt or the like. Patent Document 1 provides a friction sheet used in such a fastening and fixing structure. In this friction sheet, the surface of a metal elastic sheet is plated with diamond grains that can dig into the fastening surfaces of the fastening-target member.
For example, when a friction sheet is wedged between the fastening end surfaces of two shaft members and the fastening end surfaces are fixed in a fastened manner by a fastening bolt, the diamond grains on both sides of the friction sheet dig into the fastening end surfaces of both members and a large frictional force is produced between these fastening end surfaces. The fastening force of the two shaft members thereby increases, and a large torque can be transmitted.